The present invention relates to an optical information recording and reproducing apparatus for recording and reproducing information from an optical recording disc including a guide track which is optically detectable and preliminarily divided into a plurality of sectors.
An optical information recording and reproducing apparatus is known in the art in which the laser beam from a laser light source 1 is converged to a tiny beam spot of less than 1 .mu.m in diameter and projected onto a rotating optical recording disc coated with or having a vapor-deposited light-sensitive material, for example, and the output intensity of the beam spot is modulated with a recording signal thus ensuring real-time recording of information such as video signals or digital signals in the form of phase variations or such optical variations as reflectance or transmittance variations on the optical recording disc provided by the irregularities in its surface and also ensuring reproduction of the recorded information through the detection of the variations in the optical characteristics.
With this type of apparatus, for reasons of increasing the density of the recording tracks, ensuring the discrete partial writing or erasing of information and the like, an optical information recording and reproducing apparatus is conceivable in which the track or tracks to be recorded are preliminarily provided with an optically detectable guide track or tracks in the spiral or concentric form and a known tracking control is performed so as to cause a tiny spot of laser beam to follow the guide track thereby recording information on the selected track or reproducing the information from the selected track.
There is a known apparatus of this type in which in order to effectively utilize the recording area in the recording of digital information including variable length data, the tracks are each divided into a plurality of sectors and the recording and reproduction of information are effected sector by sector. FIG. 1 shows an example of the optical disc tracks having a sector structure. Each track is provided at its top with an index mark 1 indicative of the beginning of the track and each track includes N sectors each composed of a sector mark 2 having sector address information for identifying the sector and a data portion 3. When recording or reproducing data from the disc of this format, the sector mark of the desired sector is detected to identify it and then data is written in or read from the sector.
On the other hand, the recording dot and track pitch of the optical recording discs are on the order of 1 .mu.m and thus various defects, foreign particles and flaws caused during the manufacture of the optical recording discs (the formation of guide tracks, the manufacture of replica discs, the vapor-deposition of recording material and the formation of protective layers) or by the environments in which they are used lead to dropouts of reproduced signals. Such dropouts deteriorate the raw error rate of the optical recording disc and also severe imperfections frequently affect the tracking control thus tending to cause the tiny spot of laser beam to jump from the track it is following to another track. This track jump may also be caused by any vibration, shock or the like imparted externally to the optical head.
While the recording and reproduction of the desired section is effected by detecting its sector mark and identifying it, where the sector mark of any sector having the recroded data is rendered undetectable due to a flaw or the like necessitating to subsequently write in the sector a special signal indicative of the defective or unwanted sector, it is necessary to use means for identifying this section in some way or other. In this case, while the usual method is to write a special signal in the target sector through the use of a timer or the like in accordance with a separate reference signal such as the index mark or the sector mark of the preceding sector, it is impossible to directly identify the target sector so that if the previously mentioned track jump occurs during the interval between the separate reference signal and the target sector in the special signal writing sequence, the special signal is erroneously recorded in any sector of another track.